1. Field of Invention
The present invention relates in general to printed circuit boards (PCBs) containing glass fiber substrates. More particularly, the present invention relates to preventing conductive anodic filament (CAF) formation in PCBs by sealing discontinuities in glass fiber bundles.
2. Background Art
Printed circuit boards (PCBs) are commonly constructed of a glass cloth or other glass fiber substrate impregnated with a varnish coating (e.g., epoxy-based resin). One problem experienced with such traditional varnish/glass PCBs is known as conductive anodic filament (CAF) growth, which results from copper dissolution which emanates from the anode of an anode/cathode pair and “grows” subsurface toward the cathode of the anode/cathode pair, frequently along separated glass fiber/varnish coating interfaces. With PCBs, anode/cathode pairs are typically adjacent plated through-holes (PTHs). CAF formation causes a number of reliability issues and can result in catastrophic failure of PCBs, which in some instances can cause fires. The bond between the varnish and the substrate is understood to be an important factor in CAF formation and growth, as is the presence of water at the varnish/glass substrate interface.
A need exists for an enhanced mechanism for preventing conductive anodic filament (CAF) formation and growth in printed circuit boards (PCBs).